Apparatus and process for concentrating a liquid sterilant and sterilizing articles therewith

ABSTRACT

A method for sterilizing a device, includes the following steps: placing the article into a chamber containing an inner atmosphere; placing a solution comprising hydrogen peroxide and water into fluid communication with the chamber, the solution having a ratio of hydrogen peroxide to water; vaporizing the solution in the inner atmosphere to form water vapor and hydrogen peroxide vapor; selectively drawing water vapor from the chamber to increase a ratio of hydrogen peroxide to water in the chamber; and contacting the article with the hydrogen peroxide vapor.

[0001] This application is a continuation of U.S. application Ser. No.09/975,714 filed Oct. 11, 2001 which is a continuation of U.S.application Ser. No. 09/223,479 filed Dec. 30, 1978, now U.S. Pat. No.6,325,972. This application is also a continuation-in-part of U.S.application Ser. No. 10/284,987 filed Oct. 31, 2002 which is acontinuation of application Ser. No. 09/470,244, filed Dec. 22, 1999which is a continuation-in-part of application Ser. No. 09/105,280,filed Jun. 26, 1998, now U.S. Pat. No. 6,068,817, which is a divisionalof application No. 08/833,375, filed Apr. 4, 1997, now U.S. Pat. No.5,961,921, which is a continuation-in-part of application Ser. No.08/628,965, filed Apr. 4, 1996, now U.S. Pat. No. 6,030,579. All aboveapplications are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a process for sterilization ofmedical instruments using a liquid sterilant. More particularly, theinvention relates to a process in which sterilization is achieved byconcentrating a liquid sterilant such as hydrogen peroxide solutioninside of a sterilization chamber and sterilizing articles therewith.

BACKGROUND OF THE INVENTION

[0003] Medical instruments have traditionally been sterilized usingeither heat, such as is provided by steam, or a chemical, such asformaldehyde or ethylene oxide in the gas or vapor state. Each of thesemethods has its drawbacks. Many medical devices such as fiberopticdevices, endoscopes, power tools, etc., are sensitive to heat, moistureor both. Formaldehyde and ethylene oxide are both toxic gases that posea potential hazard to healthcare workers. Problems with ethylene oxideare particularly severe, because its use requires long aeration times toremove the gas from articles that have been sterilized. This lengthensthe sterilization cycle time undesirably.

[0004] Sterilization using liquid hydrogen peroxide solution has beenfound to require high concentrations of sterilant, extended exposuretime and/or elevated temperatures. However, sterilization using hydrogenperoxide vapor has been shown to have some advantages over otherchemical sterilization processes (see, e.g., U.S. Pat. Nos. 4,169,123and 4,169,124 which are incorporated herein by reference). Thecombination of hydrogen peroxide with a plasma provides certainadditional advantages, as disclosed in U.S. Pat. No. 4,643,876 which isincorporated herein by reference. Commercially available sterilizationdevices, such as the STERRAD® sterilization systems sold by AdvancedSterilization Systems division of Ethicon, Inc. automate the process ofinjecting a solution of hydrogen peroxide into a sterilization chamber,vaporzing the solution to provide a hydrogen peroxide vapor, contactingarticles to be sterilized with the vapor, and exciting the vapor intothe plasma stage. The hydrogen peroxide for each sterilization cycle isshipped to the location of the sterilization system, generally by air orground transportation. Preferably, as in the case with the STERRAD®brand systems, premeasured amounts of a hydrogen peroxide and watersolution are provided in sealed enclosure, such as a capsule inside of acassette housing which can be automatically opened by the system toreduce contact between the system user and the hydrogen peroxidesolution. Such cassettes are described more fully in U.S. Pat. Nos.4,817,800 and 4,899,519 incorporated herein by reference.

[0005] The sterilization of articles containing diffusion-restrictedareas, such as long narrow lumens, presents a special challenge. Methodsthat use hydrogen peroxide vapor that has been generated from an aqueoussolution of hydrogen peroxide have certain disadvantages. Onedisadvantage is that because water has a higher vapor pressure thanhydrogen peroxide, it will vaporize faster. Another disadvantage is thatbecause of its lower molecular weight, water will diffuse faster thanhydrogen peroxide in the vapor state. Because of these physicalproperties, when an aqueous solution of hydrogen peroxide is vaporizedin the area surrounding the items to be sterilized, the water reachesthe items first and in higher concentration. The water vapor inhibitspenetration of hydrogen peroxide vapor into diffusion-restricted areas,such as small crevices and long narrow lumens. Simply employing a moreconcentrated solution of hydrogen peroxide fails to adequately addressthe problem due to the difficulty in handling highly concentratedhydrogen peroxide solutions. Transportation of such solutions can beparticularly difficult. In general, such solutions are limited toconcentrations of less than 60% hydrogen peroxide, however, regulationsand the like regarding such concentrations may of course be modified inthe future. In any event, shipping and handling of highly concentratedsolutions remains impractical.

[0006] U.S. Pat. No. 4,952,370 discloses a sterilization process inwhich aqueous hydrogen peroxide vapor is first condensed on the articleto be sterilized, followed by application of a vacuum to thesterilization chamber to remove the water and hydrogen peroxide from thearticle. This method is suitable for surface sterilization, but not forsterilization of diffusion-restricted areas such as long narrow lumensbecause it depends on the diffusion of hydrogen peroxide vapor into thelumen to effect sterilization.

[0007] U.S. Pat. No. 4,943,414 discloses a process in which a vesselcontaining a small amount of a vaporizable liquid sterilant solution isattached to a lumen, and the sterilant vaporizes and flows directly intothe lumen of the article as the pressure is reduced during thesterilization cycle. This system has the advantage that the water andhydrogen peroxide vapor are pulled through the lumen by the existingpressure differential, increasing the sterilization rate for lumens, buthas the disadvantage that the vessel needs to be attached to each lumento be sterilized. In addition, water is vaporized faster and precedesthe hydrogen peroxide vapor into the lumen.

[0008] In U.S. Pat. No. 5,492,672, there is disclosed a process forsterilizing narrow lumens. This process uses a multicomponent sterilantvapor and requires successive alternating periods of flow of sterilantvapor and discontinuance of such flow. A complex apparatus is used toaccomplish the method. Because flow through of vapor is used, closed endlumens are not readily sterilized in the process.

[0009] U.S. Pat. No. 4,744,951 to Cummings attempts to address thisproblem by providing a separate prechamber connected to thesterilization chamber. Hydrogen peroxide is first admitted to theprechamber where it is concentrated in a distillation procedureemploying the differing vapor pressures of hydrogen peroxide and water.Water's higher vapor pressure allows one to select a vaporizationpressure which selectively vaporizes water from a hydrogen peroxidesolution, thus concentrating the solution. Cummings pumps air out of theprechamber and lowers its pressure to a level at which the waterpreferentially vaporizes from the hydrogen peroxide solution. The pumpwhich is evacuating the prechamber draws out the water vapor thusreleased from solution to concentrate the remaining solution. To preventthe water vapor from traveling into the narrow spaces such as endoscopelumens, Cummings carries out the concentration process in theprechamber. This adds complexity be requiring additional chambers, pumpsand valves.

[0010] Those of skill in the art, both in Cummings day, and now, wouldnot think to employ such a concentration process in the same chamber asthe sterilization occurs due to the problem of water vapor rushing toocclude the narrow lumens. In fact, the theory predicts that such aprocess would sterilize lumens less well than by simply vaporizing allof the hydrogen peroxide solution at once, because the slow vaporizationwould more efficiently block the lumen with water vapor. However, thepresent inventors have surprisingly found that concentrating thehydrogen peroxide vapor within the sterilization chamber greatlyincreases the ability to sterilize long narrow lumens over theconvention process of essentially vaporizing all of the hydrogenperoxide at once.

SUMMARY OF THE INVENTION

[0011] A method according to the present invention of furnishingconcentrated hydrogen peroxide vapor to an article comprises the stepsof: placing the article into a chamber containing an inner atmosphere;placing a solution comprising hydrogen peroxide and water into fluidcommunication with the chamber, said solution having a ratio of hydrogenperoxide to water; vaporizing the solution in the inner atmosphere toform water vapor and hydrogen peroxide vapor; selectively drawing watervapor from the chamber to increase a ratio of hydrogen peroxide to waterin the chamber; and contacting the article with the hydrogen peroxidevapor.

[0012] Preferably, the ratio of hydrogen peroxide vapor to water vaporafter the step of selectively drawing water vapor from the chamberexceeds the ratio of hydrogen peroxide to water in the solution, morepreferably by a ratio of greater than 3 to 1, and even more preferablyby a ratio of greater than 4 to 1. Preferably, the ratio by weight ofhydrogen peroxide to water in the solution prior to vaporization is lessthan 3 to 1, and more preferably less than 3:2.

[0013] In one aspect of the invention, the step of selectively drawingwater vapor from the chamber comprises placing the solution within adiffusion restricted environment in fluid communication with the chamberduring the step of vaporizing the solution. Preferably, the diffusionrestricted environment is more diffusion restricted during the step ofselectively drawing water vapor from the chamber than during a portionof the step of vaporizing the solution during which the hydrogenperoxide is vaporizing at a faster rate than the water. Preferably, thewater vapor is drawn from the chamber through one or more exhaust portswhich are physically remote from the diffusion restriction.

[0014] Preferably, the step of selectively drawing water vapor from thechamber comprises the steps of controlling the temperature and pressureof the solution during the step of vaporizing the solution to enhancevaporization of the water from solution versus vaporization of hydrogenperoxide and extracting at least a portion of the water vapor from thechamber.

[0015] Preferably, the step of selectively drawing water vapor from thechamber comprises the steps of maintaining the solution at a pressurebelow the vapor pressure of the water in the solution and above thevapor pressure of the hydrogen peroxide in the solution.

[0016] Preferably, the solution is vaporized by pumping a portion of theatmosphere out of the chamber to lower the pressure of the chamber at arate selected to control removal of the water and hydrogen peroxide fromthe solution so as to concentrate the hydrogen peroxide remaining in thechamber.

[0017] Preferably, the temperature of the solution during the vaporizingstep is held below the temperature of the atmosphere in the chamber soas to increase the vapor pressure of the water in the solution relativeto the hydrogen peroxide in the solution which enhances vaporization ofthe water from the solution in preference to vaporization of thehydrogen peroxide from the solution. Preferably, the temperature of theatmosphere in the chamber is above room temperature and the temperatureof the solution during the vaporizing step is at least 100° C. below thetemperature of the atmosphere in the chamber. Preferably, the solutionis vaporized in a vaporizer which is in fluid communication with thechamber yet thermally isolated from the chamber.

[0018] Preferably, the temperature and pressure of the solution iscontrolled during the first portion of the vaporizing step so as toselectively vaporize water from the solution and form a concentratedhydrogen peroxide solution and then during the second portion of thevaporizing step the temperature of the concentrated solution is raisedto enhance vaporizing the concentrated solution.

[0019] Preferably, the temperature and pressure of the solution iscontrolled during a first portion of the vaporizing step so as toselectively vaporize water from the solution and form a concentratedhydrogen peroxide solution and during a second portion of the vaporizingstep in which the concentrated hydrogen peroxide solution is vaporized,atmosphere is not withdrawn from the chamber.

[0020] Preferably, the chamber is dried prior to the step of vaporizingthe solution. Drying can be accomplished by pumping a portion of theatmosphere out of the chamber or by applying energy to excite moleculesof liquid water within the chamber into the gaseous or plasma state ofmatter and pumping a portion of the atmosphere out of the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a schematic diagram of a chamber and accessoriessuitable for use in the hydrogen peroxide sterilization process of theinvention.

[0022]FIG. 2 is a schematic diagram of a chamber, pump and throttlevalve for use in the hydrogen peroxide sterilization process of theinvention.

[0023]FIG. 3 is a schematic diagram of a system with one pump and twovalves, one valve having a larger pump vacuum line for quicker pumpdownand one having a smaller vacuum line for slower pumpdown.

[0024]FIG. 4 is a schematic diagram of a single valve sterilizationsystem having two pumps, one for slower pumpdown and one for quickerpumpdown.

[0025]FIG. 5 is a schematic diagram of a system with two pumps and twovalves, one pump for slower pumpdown and one for quicker pumpdown.

[0026]FIG. 6 is a schematic diagram of a system with a vaporizer.

[0027]FIG. 7 is a schematic diagram of a system with an alternativevaporizer.

[0028]FIG. 8 is a schematic diagram of a system with a furtheralternative vaporizer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Sterilizing the inside of lumened devices has always posed achallenge to sterilization systems. Copending U.S. application Ser. No.08/628,965, the entire contents of which are hereby incorporated byreference, discloses a method of hydrogen peroxide vapor sterilizationof diffusion-restricted environments, such as long narrow lumens, atpressures less than the vapor pressure of hydrogen peroxide bypretreating the article to be sterilized with a dilute solution ofhydrogen peroxide prior to exposure to a vacuum. U.S. Pat. No.5,851,485, incorporated herein by reference, controls the pumpdown rate.

[0030] An apparatus useful in the process of the present invention isshown schematically in FIGS. 1 and 2 and comprises a chamber 2, athrottle valve 4 and a pump 6. In FIG. 2, the chamber 2 is attached tothe pump 6 by the throttle valve 4. The valve 4 can be controlled eitherautomatically or manually to maintain the pressure. In the automaticmode of operation, the throttle valve 4 opens based on the pressure inthe chamber via a pressure transducer and valve controller. Such valvesare commercially available from, for example, MKS (Andover, Md.).

[0031] Hydrogen peroxide can be introduced into the system in anyfashion. In one emobdiment, a dilute, aqueous solution of hydrogenperoxide is placed in wells 8 as shown in FIG. 1. The aqueous solutionof hydrogen peroxide can also be placed within the lumen of long narrowobjects to be sterilized. As the pressure in the sterilization chamber 2is reduced, the hydrogen peroxide vaporizes and contacts the surface tobe sterilized (i.e., colonoscope 10 in FIG. 1) which is placed on metalgrid 12 which rests on tray 14. In a preferred embodiment, the tray canbe configured with a plurality of wells designed to retain a knownvolume of liquid sterilant. In one embodiment, the volume ofsterilization chamber 2 is about 18.5 liters and its dimensions areabout 22″ (55.9 cm)×4.25″ (10.8 cm)×12″ (30.5 cm).

[0032]FIG. 3 illustrates a parallel two-valve arrangement for use in thesterilization process of the invention. In this embodiment, the chamber2 is in fluid communication with the pump 6 via valves 16 and 18. Valve16 mediates the initial rapid evacuation, the first step of a two stepevacuation process. Valve 18 mediates slow evacuation, the second stepof the process, which ensures maximal contact of the article to besterilized with the vaporized aqueous hydrogen peroxide. The pumpdownrate can be controlled by the pumping speed and/or the percent openingof the valve. Either valve can be used to maintain the pressure. Inpractice, controlling the process so that all of the water evaporatesbefore any of the hydrogen peroxide evaporates is very difficult, yetthe preferential evaporation and elimination of water vapor from thesystem effectively concentrates the hydrogen peroxide therein withoutthe attendant complexity of shipping and handling concentrated hydrogenperoxide solutions prior to vaporization.

[0033] As the water evaporates from solution its voume greatly increasesthus raising the pressure in the system and requiring additional pumpingto extract the water vapor to maintain the pressure between the twovapor pressures. Also, the vapor pressures change with changingconditions within the chamber.

[0034]FIG. 4 illustrates a sterilization apparatus having two pumps 20and 22, and one valve 4. Pump 20 allows quicker pumpdown of the chamber2, while pump 22 allows slower pumpdown. FIG. 5 illustrates an alternateconfiguration having two valves 24 and 26 in fluid communication withthe pumps 20 and 22, respectively.

[0035] Regardless of which configuration is used, hydrogen peroxide canbe introduced into the chamber as a liquid. In one preferred embodiment,hydrogen peroxide is introduced as a vapor and the chamber parametersare changed so that the vapor condenses as a liquid on the surface ofinterior of an article to be sterilized. Such changes include increasingthe pressure.

[0036] The aqueous solutions of hydrogen peroxide can be relativelydilute, e.g. as low as 1-6% peroxide by weight, since sterilization isnot achieved through contact with the hydrogen peroxide solution, butrather is achieved at low temperatures (preferably 15°-80° C., morepreferably 20°-60° C., still more preferably 40°-55° C.) and in shortperiods of time (preferably less than one hour, and more preferably lessthan one-half hour) upon exposure to hydrogen peroxide under vacuum. Themethod of the present invention is particularly effective with articleshaving inaccessible or hard-to-reach places. Such articles include long,narrow lumens, hinges and other articles having spaces where diffusionof vapors is restricted. Although hydrogen peroxide is used in theexamples described herein, the use of other liquid sterilants which havevapor pressures lower than the vapor pressure of the solvent in whichthey are provided are also contemplated. Such sterilants include, forexample, aqueous peracetic acid solution and aqueous glutaraldehydesolution.

[0037] Preferably, the article to be sterilized is contacted withsterilant prior to the vaporization step to localize at least some ofthe vaporization in the diffusion restricted areas. Such contacting canbe accomplished either directly or indirectly. Direct contactingincludes methods such as static soaking, flow through, aerosol spray,condensation of a vapor. Any other methods involving physicallycontacting the articles to be sterilized with sterilant would beconsidered direct contacting. Indirect contacting includes those methodsin which sterilant is introduced into the chamber, but not directly onor in the articles to be sterilized.

[0038] At the end of the process, deep vacuum can be used to removeresidual sterilant. A plasma can also be used to both enhancesterilization efficacy and to remove residual sterilant.

[0039] The pumps shown schematically in the figures can be anycommercially available pump. Two preferred pumps are from Leybold VacuumProducts, Inc. (Export, Pa.) (Model D16A, pump rate=400 liters/min) andKNF Neuberger, Inc. (Trenton, N.J., Model N740, pump rate=45liters/min). The Leybold pump can reach a pressure of less than 0.1 torrand the KNF pump can reach a pressure of less than 10 torr.

[0040] For certain substrates being sterilized, such as nylon orpolyurethane, excess hydrogen peroxide in the system may leave aresidual which is difficult to remove. In order to avoid an excessresidual, the vapor concentration of hydrogen peroxide is preferablykept below 30 mg/l, more preferably less than 20 mg/l, and morepreferably still less than 15 mg/l. If higher vapor concentrations ofhydrogen peroxide are desired, excess residual can be removed using agas plasma. When using substrates such as stainless steel, polyethyleneor polypropylene, which do not retain a residual, there is no reason tolimit to the amount of peroxide which can be present in the vapor phasein the system during sterilization.

[0041] To further reduce water within the system, the chamber 2 may bedried prior to the introduction of hydrogen peroxide. Many means may beemployed to drive water out of the chamber. Primarily, this isaccomplished by vaporizing the water and pumping it out of the chamber.The vaporization can be accomplished with heat, plasma induction, vacuumor the like, either alone or in combination. Merely drawing a vacuumprior to introducing the hydrogen peroxide accomplishes a benficialdrying of the chamber 2. If the chamber 2 is heated during this processand if a high energy electromagnetic field is applied to urge the waterinto the plasma stage the drying is enhanced. U.S. Pat. No. 5,656,238issued on Aug. 12, 1997 to Spencer at al. and incorporated herein byreference teaches such techniques in more detail.

[0042] Vaporization of the hydrogen peroxide can be achieved using wellknown methods as described above; FIGS. 6 to 8 show several newpreferred methods. In FIG. 6, a chamber 30 is evacuated by a pump 32separated from the chamber 30 by a throttle valve 34. A vaporizer 36comprises a housing 38 in fluid communication with the chamber 30 andinto which extends a liquid feeding nozzle 40 from outside of thechamber 32. A cup 42 within the housing 38 receives hydrogen peroxidefrom the nozzle 40. The hydrogen peroxide can be vaporized as it exitsthe nozzle 40, or more preferably in a controlled fashion from the cup42 by controlling the temperature of the cup 42 and the pressure in thechamber 30. Temperature control of the cup 42 can be as simple asthermally isolating it from the chamber 30, or a more active controlsystem can be employed such a cooling coil or the like to maintain thecup 42 at a desired low temperature. Preferably, the entire vaporizer 36is thermally isolated from the chamber 30 or temperature controlled insome fashion. Lower temperatures of vaporization enhance thepreferential vaporization of water by exploiting the larger differencebetween the vapor pressures of water and hydrogen peroxide at lowertemperatures. Creating a diffusion restriction 44 between the vaporizer36 and chamber 30 enhances the preferential extraction of water vaporfrom the chamber as water vapor will more easily traverse the diffusionrestriction and be pumped out of the chamber during the vaporizationprocess. The diffusion restriction 44 may be simply reducing theclearance between the cup 42 and housing 38 through with the vapor musttravel to reach the chamber 30.

[0043]FIG. 7 shows a similar chamber 50, pump 52 and valve 54 withmodified vaporizer 56. The vaporizer 56 comprises a chamber 58 separatedfrom the chamber 50 by a diffusion restriction 60, such as a permeablemembrane. Liquid hydrogen peroxide solution enters the chamber 58through a valve 62. FIG. 8 illustrates a similar arrangement with achamber 70, pump 72, valve 74, and vaporizer 76 with a chamber 78 andvalved hydrogen peroxide solution inlet 80. Restriction of the diffusionbetween the vaporizer chamber 78 and main chamber 70 is variable. Duringinitial vaporization when primarily water is vaporizing the vapors passthrough a tight diffusion restriction 82. After the concentration of thehydrogen peroxide solution reaches a given level a valve 84 may beopened to speed the vaporization and diffusion of the concentratedhydrogen peroxide solution.

[0044] Preferably, the temperature in the chamber is no less than 5° C.nor more than 150° C., with the range of 50 to 65° C. being preferred,and the pressure should be no less than 0.01 torr, nor typically greaterthan atmosphere during the process, with the lowest vacuum beingtypically 0.4 torr and the diffusion pressure preferably being between 2and 10 torr, although other conditions within the spirit of theinvention will be apparent to those of skill in the art. During theconcentration stage, the pressure should not fall below 0.5 torr.Shorter overall cycles are preferred for convenience, with 5 minutesbeing a desirable goal, but longer times upwards of 6 hours or more maybe warranted in some circumstances.

[0045] Tables 1 and 2 illustrate the effectiveness of the presentinvention. The experiments were run on a chamber of 73 liters at 45° C.with 1780 mg of hydrogen peroxide 59% solution. The diffuser isseparated from the chamber by 12 2 mm diameter holes to effect diffusionrestriction. TABLE 1 Test Conditions Normal Process New Process StepTest A Test B Test C Test D Test E 1 Open valve Open valve Open valveOpen valve Open valve 2 Vacuum to Inject H₂O₂ at 1 atm Vacuum to 30 torrVacuum to 0.3 torr Vacuum to 0.3 torr 0.3 torr 3 Close valvevaporization & Inject H₂O₂ at 30 torr Inject H₂O₂ at Close valvediffusion 0.3 torr 4 Inject H₂O₂ at Vacuum to about Vaporization &Vaporization & Inject H2O2 at 0.3 torr 2 torr diffusion diffusion 0.3torr 5 Vaporization Close valve Vacuum to about 2 torr Vacuum toVaporization & & diffusion about 2 torr diffusion 6 Vent to 1 atmVaporization & Close valve Close valve Open valve diffusion 7 Vent to 1atm Vaporization & Vaporization & Vacuum to diffusion diffusion about 2torr 8 Vent to 1 atm Vent to 1 atm Close valve Vaporization & diffusion9 Vent to 1 atm

[0046] TABLE 2 Sterility test results(positives/samples) Normal ProcessNew Process Lumen size Test A Test B Test C Test D Test E 1 × 400 mm 2/20/2 0/2 0/2 0/2 1 × 350 mm 2/2 0/2 0/2 0/2 0/2 1 × 300 mm 2/2 0/2 0/20/2 0/2 1 × 250 mm 2/2 0/2 0/2 0/2 0/2

[0047] Monitoring of the temperature, pressure and hydrogen peroxideconditions within the chamber 30 (FIG. 6) allows the process to becontrolled more precisely. Preferably, an automated control system,preferably employing a computer processer, recieves inputs of thetemperature, pressure and perhaps also the hydrogen peroxideconcentration and calculates the optimal pressure at which to maintainthe chamber to remove the water from the hydrogen peroxide solution andfrom the chamber 30. It can also determine when the solution issufficiently concentrated. For instance, it may be desired to onlyconcentrate the solution to a certain degree so as to minimize the lossof hydrogen peroxide from the chamber, thereby minimizing hydrogenperoxide emissions from the chamber. While preferentially vaporizing thewater from the solution, some hydrogen peroxide will also vaporize.Accordingly, one may wish to balance the efficient use of the quantityof hydrogen peroxide within the solution against the goal of eliminatingall water from the solution and the chamber. By monitoring the ratio ofwater and peroxide the vapor phase, the valve 34 can be controlled toremove the vapor until the desired ratio is achieved. The ratio can bedetermined using a hydrogen peroxide monitor and a moisture monitor, orby using a hydrogen peroxide monitor and a pressure sensor and thencalculating the water using the PVRT equation and making the assumptionthat water and peroxide are essentially the only gases within thechamber 34.

[0048] It is known that certain spectra of light passing through thechamber can be measured to determine the hydrogen peroxideconcentration. One particular method is disclosed in co-pending U.S.application Ser. No. 08/970,925 filed Nov. 14, 1997, incorporated hereinby reference.

[0049] Table 3 illustrates the effects of the ratio of hydrogen peroxidevapor to water vapor in the chamber 30 on the ability to sterilize longnarrow lumens or other diffusion restricted environments. Water vaporwas first introduced into the system and then essentially pure hydrogenperoxide vapor was introduced by liberation from a solid form. The lowerconcentrations of water show no failures, whereas with the higher ratioin the last column the efficacy decreased and in one test 3 out of 3samples failed. Table 4 shows similar results by comparing asterilization process in which the concentration of hydrogen peroxide isnot increased according to the present invention with a process in whichit is increased. Table 5 shows the degree of concentration achievedaccording to the present invention. By monitoring the concentration(i.e. the ratio of hydrogen peroxide to water) during the sterilizationcycle it should be possible to achieve the long sought goal ofparametric release. One could be assured that if the properconcentration was maintained for a sufficient period of time that aparticular load of instruments placed within the chamber 30 andsterilized according to the present invention then the process would besufficiently predictable so as to allow the load to be released for usewithout further checking with a biological indicator. Typically, suchprocesses always employ a biological indicator in the load, such as witha test load of microorganisms, which is then checked to ensure thatsufficient sterilization has been achieved to kill all of the testmicroorganisms. With parametric release the time consuming process ofbiological indicators can be skipped. TABLE 3 Effect of water toperoxide ratio on efficacy Efficacy with Bacllius subtilis var. niger onSS blade in 3 mm × 500 mm BB LTU in 173L chamber Sterility results(positives/samples) Diffusion time 0.653 mg/L H₂O 3.266 mg/L H₂O 6.532mg/L H₂O (minutes) 6 mg/L H₂O₂ 6 mg/L H₂O₂ 6 mg/L H₂O₂  5 0/3 0/3 3/3 100/3 0/3 2/3 15 0/3 0/3 0/3 30 0/3 0/3 0/3

[0050] TABLE 4 (A) Effect of water to peroxide ratio on efficacy 59%solution Sterility results (positives/samples) Without Withconcentrating concentrating process process Lumen Dimension 8.43 mg/LH₂O 1.49 mg/L H₂O (Diameter) × (length) 12 mg/L H₂O₂ 7.3 mg/L H₂O₂ 1 ×400 mm 2/2 0/2 1 × 350 mm 2/2 0/2 1 × 300 mm 2/2 0/2 1 × 250 mm 2/2 0/2

[0051] TABLE 5 Concentrating the 59% peroxide solution Ratio of peroxideto water After all Before Right after peroxide concentratingconcentrating vaporize Vaporization in vaporizer 1.4:1 19:1 noneVaporization in chamber <1.4:1   0.85:1   4.9:1

[0052] The process may be further enhanced by admitting sufficienthydrogen peroxide into the system so as to force some of the vaporizedsolution to condense upon the instruments being sterilized within thesystem. As described above, the solution can be vaporized by admittingit into the system at any pressure above the vapor pressures of waterand hydrogen peroxide in the solution and then vaporized by reducing thepressure, or by admitting the solution at a pressure substantially belowthese vapor pressures whereupon it will start to vaporize thus releasinggas and increasing the pressure. In the second scenario if the pressureis then further reduced by pumping the concentration of the hydrogenperoxide in the system can be increased. This is especially true if thepressure rises to a level at least above the vapor pressure of hydrogenperoxide thereby limiting further vaporization of hydrogen peroxide fromsolution and perhaps encouraging some of the hydrogen peroxide tocondense upon objects such as instruments within the system. Some of thewater vapor would likely also condense in such event. By controlling thepressure excess water vapor would be exhausted from the system and thenthe condensed solution would re-vaporize. To the extent that suchsolution had condensed within diffusion restricted areas there-vaporization therein would further increase the concentration in thethose areas to enhance the sterilization efficacy therein. The quantityof solution admitted will primarily determine the pressure rise toinitiate such condensaation. The process is described in more detail inour co-pending application entitled “Sterilization ofDiffusion-Restricted Area by Re-Vaporizing the Condensed Vapor” filedcontemporaneously herewith.

[0053] A typical cycle might comprise placing a load of instruments (notshown) within a CSR wrapped tray within the chamber 30 and then drawinga vacuum on the chamber 30 with the pump 32 down to below 1 torr orabout 0.4 torr. An electromagnetic field applied to the chamber 30 atsuch time tends to drive any remaining water into the vapor or plasmastage so that it can be removed by the pump 32. The pump 32 can becycled or merely run continuously with the valve 34 controlling thevacuum process. Fresh dry air may be admitted to the chamber 30including raising of the pressure back to atmosphere. Preferably thehydrogen peroxide solution, preferably a 59% hydrogen peroxide solution,is admitted to the vaporizer 36 at atmospheric pressure and then thepump 32 exhausts the chamber 30 to a level at which the solution beginsto vaporize. A monitor 100 for hydrogen peroxide vapor and monitor 102(see FIG. 6) for water vapor in connection with an automated controlsystem 104 can be employed to optimize the pressure conditions toenhance the initial vaporization and exhaust of water vapor. After thesolution is sufficiently concentrated the pressure in the chamber 30 canbe further lowered to vaporize the remaining solution. The valve 32 isclosed to isolate the chamber 30 and the vaporized hydrogen peroxidesolution is allowed to diffuse throughout the chamber to contact theinstruments. Additional dry air or other gas can be admitted at thistime to help push the sterizing vapors into diffusion restricted areas,with the chamber 30 then further exhausted to resume a vacuum in therange of 2 to 10 torr. Additional admissions of air and vacuum can beemployed, especially in connection with additional admission andconcentration of hydrogen peroxide solutions. After the hydrogenperoxide vapors have diffused throughout the chamber for a sufficienttime aan electromagnetic field may be applied to drive the vapor intothe plasma stage and effect further steilization. When the field isremoved the ions formed from the hydrogen peroxide recombine as waterand oxygen, leaving little residual hydrogen peroxide. The chamber canbe raised to atmospheric pressure and the load removed.

[0054] It should be noted that the present invention is not limited toonly those embodiments described in the Detailed Description. Anyembodiment which retains the spirit of the present invention should beconsidered to be within its scope. However, the invention is onlylimited by the scope of the following claims.

What is claimed is:
 1. A method of furnishing concentrated hydrogenperoxide vapor to an article comprising the steps of: placing thearticle into a chamber containing an inner atmosphere; placing asolution comprising hydrogen peroxide and water into fluid communicationwith the chamber, said solution having a ratio of hydrogen peroxide towater; vaporizing the solution in the inner atmosphere to form watervapor and hydrogen peroxide vapor; selectively drawing water vapor fromthe chamber to increase a ratio of hydrogen peroxide to water in thechamber; and contacting the article with the hydrogen peroxide vapor. 2.A method according to claim 1 wherein the ratio of hydrogen peroxidevapor to water vapor after the step of selectively drawing water vaporfrom the chamber exceeds the ratio of hydrogen peroxide to water in saidsolution.
 3. A method according to claim 1 wherein the ratio of hydrogenperoxide to water, by weight, after the step of selectively drawingwater vapor from the chamber exceeds 3 to
 1. 4. A method according toclaim 3 wherein the ratio of hydrogen peroxide to water in saidsolution, by weight, is less than 3 to
 1. 5. A method according to claim3 wherein the ratio of hydrogen peroxide to water in said solution, byweight, is less than 3:2.
 6. A method according to claim 3 wherein theratio of hydrogen peroxide to water, by weight, after the step ofselectively drawing water vapor from the chamber exceeds 4 to
 1. 7. Amethod according to claim 1 wherein the step of selectively drawingwater vapor from the chamber comprises placing said solution within adiffusion restricted environment in fluid communication with the chamberduring the step of vaporizing the solution.
 8. A method according toclaim 7 wherein the diffusion restricted environment is more diffusionrestricted during the step of selectively drawing water vapor from thechamber than during a portion of the step of vaporizing the solutionduring which the hydrogen peroxide is vaporizing at a faster rate thanthe water.
 9. A method according to claim 7 wherein the water vapor isdrawn from the chamber through one or more exhaust ports and wherein theone or more exhaust ports are physically remote from the diffusionrestriction.
 10. A method according to claim 1 wherein the step ofselectively drawing water vapor from the chamber comprises the steps ofcontrolling the temperature and pressure of the solution during the stepof vaporizing the solution to enhance vaporization of the water fromsolution versus vaporization of hydrogen peroxide and extracting atleast a portion of the water vapor from the chamber.
 11. A methodaccording to claim 1 wherein the step of selectively drawing water vaporfrom the chamber comprises the steps of maintaining the solution at apressure below the vapor pressure of the water in the solution and abovethe vapor pressure of the hydrogen peroxide in the solution.
 12. Amethod according to claim 1 wherein the solution is vaporized by pumpinga portion of the atmosphere out of the chamber to lower the pressure ofthe chamber at a rate selected to control removal of the water andhydrogen peroxide from the solution so as to concentrate the hydrogenperoxide remaining in the chamber.
 13. A method according to claim 1wherein the temperature of the solution during the vaporizing step isheld below the temperature of the atmosphere in the chamber whereby toincrease the vapor pressure of the water in the solution relative to thehydrogen peroxide in the solution whereby to enhance vaporization of thewater from the solution in preference to vaporizing the hydrogenperoxide from the solution.
 14. A method according to claim 10 whereinthe temperature of the atmosphere in the chamber is above roomtemperature and the temperature of the solution during the vaporizingstep is at least 10° C. below the temperature of the atmosphere in thechamber.
 15. A method according to claim 13 wherein the solution isvaporized in a vaporizer which is in fluid communication with thechamber and wherein the vaporizer is thermally isolated from thechamber.
 16. A method according to claim 1 and further comprising thesteps of controlling the temperature and pressure of the solution duringa least a first portion of the vaporizing step so as to selectivelyvaporize water from the solution and concentrate hydrogen peroxidetherein to form a concentrated solution and during a second portion ofthe vaporizing step raising the temperature of the concentrated solutionand vaporizing the concentrated solution.
 17. A method according toclaim 1 and further comprising the steps of controlling the temperatureand pressure of the solution during a least a first portion of thevaporizing step so as to selectively vaporize water from the solutionand concentrate hydrogen peroxide therein to form a concentratedsolution and during a second portion of the vaporizing step notwithdrawing atmosphere from the chamber.
 18. A method according to claim1 and further comprising the step of drying the chamber prior to thestep of vaporizing the solution.
 19. A method according to claim 12wherein the step of drying the chamber comprises pumping a portion ofthe atmosphere out of the chamber.
 20. A method according to claim 18wherein the step of drying the chamber comprises applying energy toexcite molecules of liquid water within the chamber into the gaseous orplasma state of matter and pumping a portion of the atmosphere out ofthe chamber.